Scientists are warning that migrating geese and other birds at a wildlife refuge in China, means the birds could carry the devastating virus out of Asia and spread the avian flu virus further afield.
Health officials say this makes avian flu even more of a global threat than it already is and it raises the possibility of a pandemic.
United Nations scientists say as many as 5,000 dead birds have been found at Lake Qinghaihu, a protected nature reserve in western China.
Scientists Jinhua Liu of <<>>, and George Gao of the <<>> and colleagues say that the occurrence of the highly pathogenic H5N1 avian influenza virus infection in migrant waterfowl, indicates that the virus has the potential to be a global threat.
Apparently Lake Qinghaihu is a breeding center for migrant birds that congregate from Southeast Asia, Siberia, Australia and New Zealand.
This latest outbreak of the virus started in 2003 and has already killed 39 people in Vietnam, 12 in Thailand and four in Cambodia.
The <<>> says if the virus acquires the ability to pass easily from human to human it would kill millions of people worldwide.
To date this has not happened, but the influenza virus is extremely prone to mutation.
The virus, which appears to affects ducks with little harm but which kills chickens, had not before been seen to transmit among wild birds.
Gao's team say that lake Qinghaihu is one of the most important breeding locations for migratory birds that winter in Southeast Asia, Tibet and India, and say several species were infected, including the bar-headed goose, great black-headed gull, and the brown headed gull.
The wild birds apparently had diarrhea, which could mean the virus could be spread in contaminated water.
In their research Yi Guan of the <<>> and colleagues carried out a genetic analysis of the virus taken from the dead birds, and found that although the sequences appeared to have mutated slightly, it was closely related to the strain that has caused human illness in Thailand and Vietnam.